In general, the dispenser head includes a dispenser orifice where the user may recover the dispensed fluid. The head also includes a sealing closure member, e.g. in the form of a pin, that closes the dispenser orifice when the fluid present in the head is at a pressure that is lower than a predetermined threshold, and opens the orifice when the fluid present in the head is at a pressure that is higher than the predetermined threshold. The closure pin is thus controlled directly by the pressure exerted by the fluid that is put under pressure in the head by actuating the movable wall of the fluid reservoir. In order to ensure closure that is completely sealed, the dispenser head also includes resilient means for urging the closure pin against the dispenser orifice. The harder the resilient means are urged against the pin in sealing contact with the dispenser orifice, the better the sealing. In addition, the dispenser head also includes a fluid inlet in communication with the reservoir.
Thus, when the movable wall of the fluid reservoir is squeezed, the pressure of the fluid inside the dispenser head must overcome the force exerted by the resilient means in order to remove the pin from the dispenser orifice. The minimum pressure for removing the pin corresponds to the predetermined threshold. The pressure exerted by the fluid inside the reservoir and the head is identical, but varies as a function of the force exerted by the user on the movable wall of the reservoir. In contrast, the pressure forces exerted on the inner walls of the dispenser head vary as a function of the surface area on which the pressure is exerted, since a pressure force is directly proportional to the surface area on which the pressure is exerted.
A well known problem of dispenser heads mounted on reservoirs having squeezable walls is that it is necessary to squeeze the reservoir hard in order to remove the closure pin from the dispenser orifice. As a result, the fluid is then dispensed very quickly and often in uncontrollable manner. Even by squeezing the reservoir very progressively, the dispenser orifice nevertheless opens suddenly, and the fluid thus dispensed tends to be squirted out or even sprayed, which is not the desired result when dispensing cream or a paste. On the contrary, it is necessary for the fluid to be dispensed in the form of a glob or a bead.
Naturally, a solution that may be envisaged in order to solve the problem of sudden and quick dispensing is to decrease the stiffness of the resilient means that urge the pin against the orifice. That achieves dispensing that conforms more to the desired result, namely dispensing in the form of a glob or a bead. However, decreasing the stiffness of the resilient means naturally decreases the force with which the closure pin bears against the dispenser orifice so as to close it in sealed manner. As a result, the dispenser orifice is not closed in completely sealed manner, and the composition present inside the head is subject to attacks from the outside air, or from any contaminating element situated outside the container. This is unacceptable for certain fluids that are particularly fragile and/or that do not include any preservatives.
It thus turns out that it is difficult to make agreeable and appropriate dispensing compatible with closing the dispenser orifice in completely sealed manner. The force exerted by the resilient means does indeed contribute to obtaining sealed closure, but prevents the fluid from being dispensed in suitable manner. Nevertheless, it is increasingly required to combine these two requirements, particularly when it is desired to dispense a fluid that is fragile and/or that does not include any preservatives.